Skin and Blood Vessels of the Snout of the Australian Lungfish,Neoceratodus forsteri,and their Significance for Interpreting the Cosmine of Devonian Lungfishes

Improved structural and functional interpretations regarding the dermal skeleton of Paleozoic lungfishes (Dipnoi) can be derived from a direct comparison of Recent and fossil tissues. In particular, skin from the snout of adult Australian lungfish (Neoceratodus forsteri) contains horizontal plexuses and vertical capillary loops which resemble in structure, size and density components of the cosmine layer in such Paleozoic lungfishes as Dipterus valenciennesi and Chirodipterus australis. In addition to these dermal papillae, the skin of the snout also contains ampullary electroreceptors, goblet cells, compound mucus glands, and terminal branches and openings of the mechanoreceptive lateral line system. Pore canal systems of fossil lungfishes previously have been interpreted as housing electroreceptors or other cutaneous sense organs of the lateral line system. In contrast, we regard pore canal systems as evidence of a complex cutaneous vasculature involved in the deposition of mineralized tissues. Prevailing ideas on the structure and biological role of cosmine are reinterpreted, including the theory that electroreceptors played an important part in the origin of the dermal skeleton.     

The origin of novel features by changes in developmental mechanisms: ontogeny and three‐dimensional microanatomy of polyodontode scales of two early osteichthyans

Recent advances in synchrotron imaging allow us to study the three‐dimensional (3D) histology of vertebrate fossils, including microfossils (e.g. teeth and scales) of early jawed vertebrates. These microfossils can often be scanned at submicron resolution (<1 µm) because of their small size. The resulting voxel (3D pixel) stacks can be processed into virtual thin sections revealing almost every internal detail of the samples, comparable to traditional thin sections. In addition, 3D models of the internal microanatomical structures, such as embedded odontodes and vasculature, can be assembled and examined in situ. Scales of two early osteichthyans, Psarolepis romeri from the Early Devonian of China and Andreolepis hedei from the Late Silurian of Sweden, were scanned using propagation phase‐contrast synchrotron X‐ray microtomography (PPC‐SRµCT), and 3D models of internal canal systems and buried odontodes were created from the scans. Based on these new data, we review the evolutionary origin of cosmine and its associated pore‐canal system, which has been long recognized as a synapomorphy of sarcopterygians. The first odontode that appeared during growth shows almost identical morphology in the two scales, but the second odontode of the Psarolepis scale shows a distinctive morphology with several pores on the surface. It is suggested that a shift from ridge‐like odontode to pore‐bearing odontode was the key step in the origin of cosmine, which was then elaborated further in more‐derived sarcopterygians. We perform a detailed comparison between the two scales and propose a primary homology framework to generate microanatomical characters, which can be used in the phylogenetic analysis of early osteichthyans when more 3D data become available. Our results highlight the importance of 3D data for the study of histology and ontogeny of the dermal skeleton of early jawed vertebrates, especially scales of the polyodontode type. The traditional microvertebrate collection is not only useful for biostratigraphic studies, but also preserves invaluable biological information about the growth of vertebrate hard tissues. Today, we are only beginning to understand the biological meaning of the new 3D data. The increasing availability of such data will enable, and indeed require, a complete revision of traditional palaeohistological studies on early vertebrates.     

The Latero-sensory Component of the Dermal Skeleton in Lower Vertebrates and Its Phyletic Significance

Ørvig, T. (Section of Palaeozoology, Swedish Museum of Natural History, Stockholm, Sweden.) The latero-sensory component of the dermal skeleton in lower vertebrates and its phyletic significance. Zool. Scripta 1(3–4): 139–155, 1972.–A latero-sensory component of the dermal skeleton is met with not only in teleostomian fishes, but also in arthrodires, holocephalians (the lateral line canal “rings”), some fossil selachians, bradyodonts and acanthodians, and a few, at least, of the Osteostraci. Although not yet traceable with certainty in the Heterostraci, such a component probably existed even in early stages of vertebrate history. The persistence in the adult of this component as separate ossicles embracing the lateral line canals is surely the result of regression or other modifications of the dermal skeleton in fishes like arthrodires, coelacanthids and actinopterygians, but is apparently a primitive feature in e.g. acanthodians. In discussing the phyletic relations between the latero-sensory and membranous components of the dermal skeleton, it is concluded that these probably were separate formations from the very beginning. A condition (exemplified by certain acanthodians) where separate latero-sensory ossicles of the lateral line canals are surrounded by a mosaic of small scales of membranous origin is presumably that from which the various dermal bone-patterns in lower vertebrates are all derived. A discussion is also included in this paper of the scales and otoliths in acanthodians.     

Early larval ontogeny of the Permo-Carboniferous temnospondyl Sclerocephalus

The early larval development of the temnospondyl Sclerocephalus sp. is analyzed, based on 38 specimens from the Lower Rotliegend (Permo-Carboniferous boundary) of the Saar-Nahe Basin (south-west Germany). The study focuses on the smallest larval specimens, which exemplify changes in both proportions and ossification patterns. In comparison with dissorophoid larvae, the skull ossifies more fully and at a much faster rate; the smallest specimens already have completely formed circumorbital bones that are sutured throughout. Sculpturing undergoes two marked changes, first from uniformly pitted to pits of variable size and regional differentiation, and finally to the origin of ridges. The palate of small larvae differs from that of larger specimens in patterns of dentition, having more teeth including a denticle field on the cultriform process. The mandible of small larvae is described for the first time, being narrower than in adults and having three dentigerous coronoid elements. The smallest specimens have poorly ossified neural arches, lack vertebral centra, and have faintly ossified humeri, femora, and very poorly developed distal elements. The posterior ribs, metapodia, and phalanges appeared after the dermal elements of the pectoral girdle, whereas the scapulocoracoid and ischium are absent throughout the larval period. Early growth and differentiation of the limbs and the ilium illustrates the developmental patterning of the appendages, which proceeded from proximal to distal. Dermal squamation is uniform in small stages, consisting of round or oval osteoderms with pronounced growth rings; in large larvae, they start to differentiate in certain body regions.     

Ultrastructure of the integumental melanophores of the South American lungfish (Lepidosiren paradoxa) and the African lungfish (Protopterus sp.)

The integumental melanophores of two genera of lungfish, Lepidosiren paradoxa and Protopterus sp. were examined by light and electron microscopy. Both species possess both epidermal and dermal melanophores with fine structural characteristics basically similar to those of other vertebrates. The epidermal melanophores of both species are located in the intermediate epidermis, and possess thin perikarya containing round nuclei, and slender dendrites extending into the nearby intercellular spaces. The dermal melanophores occur immediately beneath the basement membrane, and possess flat perikarya and dendrites running horizontally between the collagen fibers of the dermis. The integument of both species does not possess an epidermal melanin unit or a dermal chromatophore unit. As in other vertebrates, each melanophore contains numerous oval, electron-opaque melanosomes, relatively large mitochondria, vacuolar endoplasmic reticula, and groups of RNP particles. Although micro filaments running randomly between other organelles occur regularly, microtubules were not demonstrated. Premelanosomes at various stages of differentiation were best illustrated in the dermal melanophores of Protopterus, and it is concluded from the observation of their fine structure that the morphological development of lungfish melanosomes closely parallels that of higher vertebrates. On the basis of melanophore morphology, Lepidosiren and Protopterus appear to be more closely related to each other than to Neoceratodus.     

Sclerotic plates or circumorbital bones in early jawed fishes?

Abstract: Circumorbital dermal bones are found in most groups of early vertebrates that have dermal bony plates on the head. Taxonomic distribution of dermal sclerotic plates on the eye itself is less clear, partly because the eyeball is rarely preserved and sometimes because sclerotic bones have been misinterpreted as circumorbital bones. Based on the examination of climatiid Climatius plus mesacanthid, cheiracanthid and acanthodid acanthodiform acanthodians, we conclude that most, if not all, acanthodiforms and climatiids had sclerotic rings. Presence and number of these elements should be included as a character in phylogenetic analyses of early jawed vertebrates.     

Heimenia在我国的发现

<正> 1984年作者在整理人民来信时发现一件很有趣的标本.从它的特殊形态特征和表面覆盖有发亮的整列层使人一眼就能看出它是属于总鳍鱼类的.经过细心的修理和进一步观察,认为属于Heimenia.标本记述材料一件保存不完整的鳞片.化石编号V7143.时代与产地云南鲁甸德红,中泥盆统海口组.     

Comparative morphology and scale formation in four species ofOncorhynchus during early life

Morphological divergence including scale formation in alevin and juvenile stages of masu (Oncorhynchus mason), coho (O. kisutch), chum (O. keta) and pink (O. gorbuscha) salmons reared in freshwater was investigated. Chum and coho salmons developed faster than the other species when raised at constant water tempertaure. Growth decreased suddenly at emergence from the gravel bed in all the four species. Morphology changed significantly from hatch through emergence to squamation. Two distinct morphological types were identified: the rotund type (masu and coho), and the streamlined type (chum and pink salmons). The former had well-developed parr marks, a deeper body and caudal peduncle, and higher relative growth coefficients, while the latter had parr marks which appeared only temporarily or never appeared, a slimmer body and caudal peduncle, and a more gradual and continuous change in morphology. Coho and chum developed squamation and formed circuli on scales considerably earlier than masu and pink salmons.     

Pigment cell refugia in homeotherms--the unique evolutionary position of the iris.

Homeotherms are generally considered to lack classical active dermal pigment cells (chromatophores) in their integument, attributable to the development of an outer covering coat of hair or feathers. However, bright colored dermal pigment cells, comparable to chromatophores of lower vertebrates, are found in the irides of many birds. We propose that, because of its exposed location, the iris is an area in which color from pigment cells has sustained a selective advantage and appears to have evolved independently of the general integument. In birds, the iris appears to have retained the potential for the complete expression of all dermal chromatophore types. Differences in cell morphology and the presence of unusual pigments in birds are suggested to be the result of evolutionary changes that followed the divergence of birds from reptiles. By comparison, mammals appear to have lost the potential for producing iridophores, xanthophores, or erythrophores comparable to those of lower vertebrates, even though some species possess brightly colored irides. It is proposed that at least one species of mammal (the domestic cat) has recruited a novel iridial reflecting pigment organelle originally developed in the choroidal tapetum lucidum. The potential presence of classical chromatophores in mammals remains open, as few species with bright irides have been examined.     

Pigment Cell Refugia in Homeotherms—The Unique Evolutionary Position of the Iris

Homeotherms are generally considered to lack classical active dermal pigment cells (chromatophores) in their integument, attributable to the development of an outer covering coat of hair or feathers. However, bright colored dermal pigment cells, comparable to chromatophores of lower vertebrates, are found in the irides of many birds. We propose that, because of its exposed location, the iris is an area in which color from pigment cells has sustained a selective advantage and appears to have evolved independently of the general integument. In birds, the iris appears to have retained the potential for the complete expression of all dermal chromatophore types. Differences in cell morphology and the presence of unusual pigments in birds are suggested to be the result of evolutionary changes that followed the divergence of birds from reptiles. By comparison, mammals appear to have lost the potential for producing iridophores, xanthophores, or erythrophores comparable to those of lower vertebrates, even though some species possess brightly colored irides. It is proposed that at least one species of mammal (the domestic cat) has recruited a novel iridial reflecting pigment organelle originally developed in the choroidal tapetum lucidum. The potential presence of classical chromatophores in mammals remains open, as few species with bright irides have been examined.     

Evolution of cis-Acting Elements in 5′ Flanking Regions of Vertebrate Actin Genes

Regulation of the vertebrate actin multigene family involves the recognition of various regulatory sequences (cis-acting elements) that specify the distinct tissue type and developmental program of expression for each actin paralogue, which implies that the distribution of cis-acting elements may be unique for each paralogue gene. To elucidate the evolution of these unique distribution patterns, we improved a method to scan for cis-acting elements in the 5′ flanking regulatory region of genes and used it to analyze five cis-acting elements (SRE, MyoD binding site, Elk-1 binding site, positive and negative YY1 binding sites) of six actin paralogue genes (β and γ cytoplasmic actins, α and γ smooth muscle actins, and α skeletal and α cardiac actins) among various vertebrates. It was shown that although an element(s) may exist in all paralogue genes of the same species, its numbers, compositions, and distribution patterns or even sequences vary remarkably among paralogues, which contributes to their different tissue- and developmental-specific expression. However, each pair of coexpressed paralogues has some certain similarity in distribution patterns. Furthermore, among various orthologues of actin genes derived from diverse vertebrates, the sequences, numbers, and distribution patterns of these cis-acting elements are highly conserved or even identical in the long run of phylogeny of vertebrates. Taken together, the results described above strongly indicate that not only the structures of actins but also their expression patterns are essential in both the phylogeny and the physiology of vertebrates. The distribution patterns of cis-acting elements of various actin genes can be regarded as indicators of both horizontal (paralogous) and vertical (orthologous) evolution of actins. Received: 1 March 1999 / Accepted: 6 August 1999     

Relationships between squamation chronology of the bluegill, Lepomis macrochims Rafinesque, and age-growth methods

Scales first developed on 13 mm juvenile bluegills along the midlateral line anterior to the caudal fin in the area of the caudal peduncle, squamation chronology continued anteriorly, and was completed in the dorsal area of the nape of 25 mm bluegills. Body-scale relationships calculated from scales taken from three distinct body regions of adult fish were compared using both the Dahl-Lea and the Fraser-Lee methods. The calculated body length intercepts followed the chronology of the squamation and compared closely with the observed fish length at scalation of each area. The body length intercepts were different from one another and from the origin. There was little difference among the Dahl-Lea and Fraser-Lee calculated lengths beyond annulus one for the three distinct body regions. In all cases, however, results from the Dahl-Lea method produced lower lengths than their corresponding values calculated by the Fraser-Lee method. Selected size classes which omitted the smaller fish resulted in body length intercepts higher than those calculated from the total sample regression.     

Formation of dermal skeletal and dental tissues in fish: a comparative and evolutionary approach

Osteichthyan and chondrichthyan fish present an astonishing diversity of skeletal and dental tissues that are often difficult to classify into the standard textbook categories of bone, cartilage, dentine and enamel. To address the question of how the tissues of the dermal skeleton evolved from the ancestral situation and gave rise to the diversity actually encountered, we review previous data on the development of a number of dermal skeletal elements (odontodes, teeth and dermal denticles, cranial dermal bones, postcranial dermal plates and scutes, elasmoid and ganoid scales, and fin rays). A comparison of developmental stages at the tissue level usually allows us to identify skeletogenic cell populations as either odontogenic or osteogenic on the basis of the place of formation of their dermal papillae and of the way of deposition of their tissues. Our studies support the evolutionary affinities (1) between odontodes, teeth and denticles, (2) between the ganoid scales of polypterids and the elasmoid scales of teleosts, and (3) to a lesser degree between the different bony elements. There is now ample evidence to ascertain that the tissues of the elasmoid scale are derived from dental and not from bony tissues. This review demonstrates the advantage that can be taken from developmental studies, at the tissue level, to infer evolutionary relationships within the dermal skeleton in chondrichthyans and osteichthyans.     

Heterogeneity of the cellular sources of restorative processes in vertebrates

Possible cell sources for restorative processe in adult vertebrates have been considered: (1) differentiated cells undergoing a certain reconstruction after the organ damage; (2) reserve of little-differentiated cells which can be represented by heterogenous populations. Experimental data obtained on a few most studied models of restoration of the damaged organs or their parts have been analyzed. Each particular restorative process can be realized by cell populations which differ from each other by a number of features: origin, potencies, way of formation, localization of cambium, etc. Participation of heterogenous cell populations is most pronounced upon stimulation of restorative processes and in the extreme conditions. Specific involvement of every possible cell source in a particular case of restoration depends on the organism's properties, peculiarities of the damaged organ, as well as on conditions of damage. The existence of diverse cell sources provides for certain reserves of restoration what appears to be indispensable for reliability of restorative processes in varying conditions of damage.     

Conchodontus,Mitrellataxis and Fungulodus: Conodonts,fish or both?

Conchodontus, Mitrellataxis and Fungulodus are phosphatic microfossils from the Late Devonian of China and North America, alternatively interpreted as conodont elements or fish scales. The histology and microornament of these sclerites have been studied in an attempt to resolve their affinity, and to determine characters for distinguishing between conodont elements and the ichthyoliths of other lower vertebrates. The histology of all three genera is directly comparable to conodont elements, dispelling the notion that conodonts are histologically indistinguishable from the teeth and scales of other vertebrates. Microornament is found not to be useful in discriminating between high-level taxonomic groupings. White matter and thickness of prismless enamel are suggested as apomorphies of the Conodonta.     

Ultrastructure of the integumental melanophores of the coelacanth,Latimeria chalumnae

The integumental melanophores of Latimeria chalumnae were studied by light and electron microscopy. The epidermal melanophore located in the mid-epidermis consists of a round perikaryon with long slender dendrites extending into epidermal cells and intercellular spaces. The dermal melanophores occur in the loose dermal matrix underlying a relatively thick layer of collagen fibers. The dermal melanophores are usually flattened and their dendrites lie parallel to the collagen layer. Both epidermal and dermal melanophores contain oval, electron-opaque melanosomes, large mitochondria, agranular vacuoles of endoplasmic reticulum and microtubules. Microfilaments and RNP particles are less conspicuous. While the peripheral cytoplasm of both dermal and epidermal melanophores is filled with a large number of melanosomes, the perinuclear cytoplasm of many dermal melanophores is occupied by premelanosomes in various stages of differentiation, and that of the epidermal melanophore contains numerous large vacuoles. Despite the scarcity of epidermal melanophores, the epidermal melanin unit is present in the form of melanosome complexes. In addition, the melanophores of Latimeria possess the basic characteristics common to other vertebrates, but they more closely resemble those of lungfish and other aquatic vertebrates.